A motor vehicle comprises, in a known way, a plurality of on-board computers, each of which can be used to control one or more pieces of equipment of the vehicle, notably operating parameters of the engine (such as fuel injection), electrical parameters of the vehicle, the power-assisted steering system of the vehicle, and others.
Conventionally, an on-board computer takes the form of a case in which a printed circuit is mounted, the case being intended, notably, to protect the printed circuit from impact and sprays of water.
In a known way, the electronic components of the printed circuit give off heat when in use, causing a rise in the temperature and pressure inside the case. This rise in temperature and pressure may damage the electronic components of the printed circuit, creating a serious problem.
It has therefore been proposed that a ventilation filter be mounted on the case, in an opening formed for this purpose through a wall of the case to allow air to pass between the inside and the outside of the case, while preventing the penetration of water into the case.
The document EP 1 786 251 A2 discloses a case on which a first type of ventilation filter is mounted. This filter takes the form of a plastic plug composed of an air flow tube to which a protective member is fastened. This air flow tube comprises a first end mounted in the opening of the case and a second end, at which end a membrane, configured to allow air to flow between the inside and the outside of the case, is mounted. The protective member enables the membrane to be protected, notably, from high-pressure water sprays that may strike the case during the standard strength tests that are conducted on this type of computer. For this purpose, the protective member takes the form of a cylindrical cap of circular section, the diameter of which is greater than the diameter of the tube, so that the tube is completely covered. This cap is closed at one end, to protect the membrane from high-pressure water sprays, and is partially open in its lower part, to allow air to flow through the membrane.
However, this type of filter is both difficult and expensive to manufacture and mount on the case, which is a considerable problem. Consequently, a second ventilation filter solution has been proposed, in which a portion of the case is modified by stamping, to form an opening at the end of the stamped portion and air flow channels extending into the stamped portion from the opening. A ventilation membrane is mounted directly in the opening, and a protective membrane, in the form of a rectangular plate pierced at its corners, is mounted on top of the stamped portion so as to protect the membrane from high-pressure water sprays while allowing air to flow in the channels.
However, it has been found that high-pressure water sprays may pass through the pierced corners of the protective plate, flow into the channels and reach the membrane at a pressure of more than 0.83 bar, which may damage the membrane, notably by detachment or delamination. Such damage may allow water to reach the printed circuit, resulting in the aforementioned problems.